He and his family moved to California when he was very young. At an early age, Jason began studying the piano. As his musical skills improved, he got jobs playing occasional weddings. He did not consider acting until high school, when he served as an emergency replacement in Whodunnit? He knew from then on that he wanted to be an actor. His father had a friend who was a theatre manager and he happened to be in the audience that night, who helped him get other jobs.

He is best known for his role as Shawn-Douglas Brady on the soap opera Days of Our Lives, a role he has been playing since 1999. His other credits include the film The Wizard of Loneliness and the TV movie Club Med.

In 2005, Cook was arrested in a Des Moines, Iowa airport for drug possession and public intoxication.